1. Field of the Invention
The invention relates to a Schmitt-trigger circuit for converting an input signal on an input terminal into an output signal on an output terminal, which circuit comprises a differential amplifier comprising a first transistor and a second transistor, each having a base, an emitter and a collector, the emitters of the first and the second transistor being coupled to a first current source, the base of the first transistor being coupled to the input terminal, the collector of the second transistor being coupled to an input of a first current mirror, and the base of the second transistor being coupled to an output of the first current mirror.
2. Description of the Prior Art
A Schmitt-trigger circuit comprising two emitter-coupled transistors is known from Japanese Kokai No. 60-136413(A). The input voltage is applied to the base of one transistor (first input). The second input, i.e. the base of the second transistor, is connected to the collector of the second transistor by a current mirror. The first and second transistor have their emitters connected to a current source.
The known Schmitt-trigger circuit cannot readily be fabricated in integrated circuit technology, because resistors, in particular those having high values, are difficult to integrate.